Methods have been devised for dispensing mercury or other materials with high vapor pressure characteristics in a gas-filled discharge tube such as a fluorescent lamp. Reference is now made to U.S. Pat. No. 3,684,345 which is directed to a method of dispensing mercury in connection with a gas-filled discharge tube, particularly a number indicator tube operating on the glow principle. Typically, the mercury or the like material is inserted into a capsule or ampule and the capsule is then inserted into the envelope of the tube. At the desired moment during the manufacturing process, mercury is released by destroying or deforming the ampule. In this regard, mention is made in U.S. Pat. No. 3,684,345 of a technique employing a heating coil for causing a softening and opening of the glass capsule. The inventive concepts described in the aforementioned patent relate to the use of the energy of a high intensity infrared radiation source. In this regard, the mercury containing ampule is fabricated from infrared absorbing glass, such as, for example, Corning glass No. 9362 having an outer diameter of 0.15" and an inner diameter of 0.10". This glass is highly absorbing to radiation in the region of one micron and when mounted inside glass tubing typically used for fluorescent lamp jackets, i.e. non-infrared absorbing material, the ampule can be heated to its softening point without any damage to the fluorescent glass tubing.
Thus, an incandescent light source may be utilized to open glass capsules containing mercury and disposed within processed fluorescent lamps. However, depending upon the volume of the capsule and the mass of the mercury, it has been found that for a relatively small ratio of the mass of mercury to the inner capsule volume, problems come about in being able to properly and accurately break (burst) and open the capsule.